Generally, gas turbine engines have three main sections or assemblies, including a compressor assembly, a combustor assembly, and a turbine assembly. In operation, the compressor assembly compresses ambient air. The compressed air is channeled into the combustor assembly where it is mixed with a fuel and ignites, creating a heated working gas. The heated working gas is expanded through the turbine assembly. The turbine assembly generally includes a rotating assembly comprising a centrally located rotating rotor and a plurality of rows of rotating blades attached thereto. A plurality of stationary vane assemblies, each including a plurality of stationary vanes, are connected to a casing of the turbine assembly and are located interposed between the rows of rotating blades. The expansion of the working gas through the rows of rotating blades and stationary vanes in the turbine assembly results in a transfer of energy from the working gas to the rotating assembly, causing rotation of the rotor. The rotor further supports rotating compressor blades in the compressor assembly, such that a portion of the output power from rotation of the rotor is used to rotate the compressor blades to provide compressed air to the combustor assembly.
It has been determined that during engine load-up and shut down procedures, high amounts of stress induced by a thermal gradient may cause cracking of the engine casing proximate to an interface between a compressor/combustor casing and the turbine casing. Specifically, during engine load-up, the temperature of air inside the engine casing proximate to the interface between the compressor/combustor casing and the turbine casing rises very quickly, i.e., the temperature increases from ambient temperature to around 400° Celsius in about 20 minutes, while the temperature of the air outside of the engine casing rises much more slowly, i.e., the temperature may take several hours to substantially increase. Since cracking of the engine casing may result in expensive and time consuming repair procedures, it would be desirable to provide a structure for reducing the amount of stress induced on the engine casing in the areas susceptible to the cracking.